The invention relates to the production of aconitic acid and in particular to the production of aconitic acid by fermentation.
Aconitic acid is a naturally occurring acid being present in Aconitum and other genera of plants, including beet roots and sugar cane. It can be prepared from the calcium magnesium salt recovered from sugar cane juice and from molasses. Aconitic acid is also manufactured commercially by dehydration of citric acid. Aconitic acid is an intermediate of the tricarboxylic acid cycle and as such is produced by many microorganisms. However, it does not normally accumulate insignificant amounts. It has been alleged that aconitic acid is produced by fermentation of Aspergillus niger in the presence of methylene blue (Sakaguchi and Baba, Bull. Ag. Chem. Soc. Japan, 1942, 18, no. 12, 1127-1130, English abstract 95), but no fermentation process for the production of aconitic acid on a commercial scale has ever been developed.
Aconitic acid is an unsaturated tricarboxyic acid and is therefore potentially useful as a co-monomer which, by virture of its carboxylic functionality, confers specific properties on polymeric materials in which it is incorporated. In the form of its esters, it also finds specialised use as a plasticiser for synthetic rubber and other polymeric materials such as polyvinyl chloride. However, such uses have not been very extensive, due to the high cost of manufucture. If a cheaper method of manufacture could be found, then such uses would become more attractive and further uses would become economic. A review of uses of aconitic acid has been published by Miller and Cantor, in "Advances in Carbohydrate Chemistry", 1951, 6, 231-249.
We have now discovered that certain mutant strains of Aspergillus terreus are capable of producing aconitic acid in good yield by fermentation of suitable carbohydrate substrates, including sucrose or glucose. Presently known strains of Aspergillus terreus produce predominantly itaconic acid from such substrates. We believe, moreover, that mutant strains of other itaconic acid producing Aspergillus species, e.g. Aspergillus itaconicus, could also be found which would be capable of producing aconitic acid in good yield.
We have also found that, if the production (or activity) of aconitase in the fermentation medium is inhibited, e.g. by adding a fluoroacetate, such mutant strains will produce citric acid in significant yield. Other methods of inhibiting the production (or activity) of aconitase would clearly have the same effect.